David Spiegelhalter, Winton professor for the public understanding of risk2

1London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK

2University of Cambridge, Cambridge, UK

ben.goldacre{at}lshtm.ac.uk

Canadian legislation had minimal effect on serious head injuries

We have both spent a large part of our working lives discussing statistics and risk with the general public. We both dread questions about bicycle helmets. The arguments are often heated and personal; but they also illustrate some of the most fascinating challenges for epidemiology, risk communication, and evidence based policy.

With regard to the use of bicycle helmets, science broadly tries to answer two main questions. At a societal level, “what is the effect of a public health policy that requires or promotes helmets?” and at an individual level, “what is the effect of wearing a helmet?” Both questions are methodologically challenging and contentious.

The linked paper by Dennis and colleagues (doi:10.1136/bmj.f2674) investigates the policy question and concludes that the effect of Canadian helmet legislation on hospital admission for cycling head injuries “seems to have been minimal.”1 Other ecological studies have come to different conclusions,2 but the current study has somewhat superior methodology—controlling for background trends and modelling head injuries as a proportion of all cycling injuries.

This finding …

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